SCSI-3 Cable Questions

Gerry Houlder Gerry_Houlder at notes.seagate.com
Tue Dec 5 09:26:55 PST 1995


I believe the intent of the signal placement guidelines (that specify which 
pairs go into which layers) is that it is more important to specify the layers 
for S/E use rather than Differential use. The S/E signals are more sensitive to 
crosstalk and impedence variations, and the S/E impedence value is much lower 
than the differential impedence value.

Thus when the resulting round cable is used in a S/E system, the REQ and ACK 
have the proper seperation from the data lines to prevent crosstalk problems. 
When that same cable is used with differential drivers, the crosstalk and 
impedence variance problems are small enough to not matter; therefore the REQ 
and ACK don't have to be in the core.

Do you have any issues with this, other than just to make sure the committee 
wasn't misstating its intent?




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